Benjamin Hawkins, and the phrase would be correctly written as 'God willing and the Creek don't rise'. Hawkins, college-educated and a well-written man would never have made a grammatical error, so the capitalization of Creek is the only way the phrase could make sense. He wrote it in response to a request from the President to return to our Nation's Capital and the reference is not to a creek, but The Creek Indian Nation. If the Creek "rose", Hawkins would have to be present to quell the rebellion. I believe that the phrase is somewhere in his preserved writings.
And now we know.